LOS ANGELES  The difference between owning a ferret in Hawaii and one in Pennsylvania can be up to three years in jail — and hundreds of thousands of dollars in fines.

That’s the penalty for ferret fans in the Aloha State, where the 3-pound members of the weasel and polecat family are banned amid concerns of the animals escaping and wreaking havoc on the islands’ delicate ecosystems. Similar fears are behind a decades-old ban in California, which has one of the nation’s most diverse ecosystems.

“The concern is that if these animals were released, like other nonnative species have been, they would adapt and thrive and out-compete native species for food, and prey on native species,” said Adrianna Shea, deputy director of California’s Fish and Game Commission.

States have had problems with feral animals in nonnative environments, creating problems for native species by eating them or ravaging their food supply. Feral cats, for example, have decimated bird populations.

But ferret fans argue that the foot-long domesticated creatures make excellent pets and shouldn’t be regulated by wildlife agencies.

“Ferrets are really wonderful animals for those of us who are so inclined. They are messy, and they’re expensive, and they’re demanding, but they are full of personality, full of love and full of joy,” said Pat Wright, who lives in La Mesa, and has been fighting California’s ban for nearly 20 years.

Keeping a ferret as a pet takes more time, care and money than owning a dog or cat. The American Veterinary Medical Association in Schaumburg, Ill., which recently posted a YouTube video on pet ferrets, noted that they need to be caged most of the time, require hours of exercise and emit a musky odor that many people find unpleasant. Large cages are expensive, but on the other hand, ferrets don’t require as much medical or dental care as cats or dogs.

“They are wonderful little clowns that not only steal your heart but they will steal anything they deem is theirs. This includes your shoes, socks, pens, pencils, hairbrushes, potatoes, car keys, wallets and clothing. I had two ferrets that tried to take my notebook computer to what is called their hidy-hole,” said AmyJo Casner of Harrisville, Pa., who legally owns ferrets Manny, Marcuz and Marylin.

A count of ferret owners across the U.S. was unavailable, but the American Pet Products Association said that in 1992, 2 percent of people who owned a small animal like a mouse, rat, ferret, gerbil, rabbit, hamster or guinea pig said they had a ferret. In 2000, 10 percent of small-animal owners said they had a ferret, and 7 percent in 2010 had them. That’s despite bans in the two states, plus a number of large cities, including New York, and U.S. military bases.

In California, where having a ferret can net a $500 fine or six months in jail, Wright estimated that between 50,000 and 500,000 pet ferrets live a clandestine existence. His guess is based on ferret-supply sales and a 5,000-member mailing list for his ferret legalization cause.